Black Horse Sukhoi Su-31

[thunder1]

Here's my Sukhoi Su-31 I converted to electric. It is from Black Horse Models but I believe it's the same as the Pheonix Models Su-31. The model is extremely sturdy. Originally designed for a .46 glow motor I decided to try out the AXI 2826/10 motor I already had with 4s2p 4000 mAH lipos. It turned out to be about 6 lbs so the power is pretty marginal with the mid size AXI. I'm pushing 500 watts through it but that's still not enough for a Sukhoi. I've ordered a Cyclon 60 and will use that with a 5s2p pack of the same cells. At 750 watts it should have some hustle.

I maidened it with the recommended control throws and the CG in the middle of the recommended range. It was so pitch sensitive I barely brought it down in one piece. It also just didn't want to descend with the motor off. I adjusted the control thros to 30% and flew it again. It was manageable but still wouldn't glide well and it snap rolled when I gave full elevator at high speed (around 7mm, recommended was 15)

I felt it was tail heavy so I took it home and put in the 5s pack instead of the 4s pack. It then balanced at the front of the CG range listed, 100mm. The power was a lot better but it would still snap and not glide well. I was flying low and slow, practicing landings over the tall grass at the edged of my club's field when the model snapped and went down nose-first into the tall (~3feet) grass. It was going so slowly that I didn't expect any damage and I was right. Not even a scratch. They build these things pretty sturdy!

The battery had been mounted to the front of the firewall. So I attached the packs (2 - 2s and 2 - 3s packs with a wiring harness) to the sides of the cowl to move the CG even farther forward. It balances at about 92mm fron the leading edge now so I hope that will tame the pitch sensitivity. I love a snappy plane but I also like to be able to bring it down without having to fly it into the ground.

I haven't flown it in this configuration yet. I will be able to move the batteries back to the firewall once I get the new Cyclon 60 motor since it's a couple ounces heavier. The batteries held on very well to the firewall on the crash I had. I don't know if they would have done as well on the sides of the cowl as they are now mounted. The cowl would have taken a lot of (unnecessary) force.

I really like the looks of this model and it handles the wind well. I printed the Breitling decals out using clear inkjet waterslide decals. I'm not sure why the manufacturer didn't use the same decals. They had some funkey black SU-31 and Sukhoi decals all over the place. The blue diamonds on the bottom look funny to me as well but the first flight proved they are a great orientation aid. So I'll leave them in place.

Here's some pictures:

[wellington53]

Nice, I need to do something like this one day!

Glenn.

[CUBANO8]

I felt it was tail heavy so I took it home and put in the 5s pack instead of the 4s pack. It then balanced at the front of the CG range listed, 100mm. The power was a lot better but it would still snap and not glide well. I was flying low and slow, practicing landings over the tall grass at the edged of my club's field when the model snapped and went down nose-first into the tall (~3feet) grass. It was going so slowly that I didn't expect any damage and I was right. Not even a scratch. They build these things pretty sturdy!


I have seen and heard of these planes doing this. Some guys at the field they move the CG forward, and reduce the throws.

Good Luck
Sam

[the Swamp Fox]

Congrats Thunder,

excellent report and nice pics !

hope you get her dialed in .

continued good luck~

[thunder1]

SF, Thanks.
I had another flight today. It still seems tail heavy.
I've run the numbers through the CG calculator here: http://www.palosrc.com/instructors/cg.htm and come up with 3.32" from the leading edge to get the CG to 30%. The stock CG location is around 38%! Too wild for me. I'm currently at 35%. I've got to get more weight up front to move the CG even farther forward. I think I'll move the motor a little farther forward.

[the Swamp Fox]

Thanks for the link . That will certainly come in handy .

Hope the Cyclone 60 works out . good price on that one . look forward to a report ...

The batteries held on very well to the firewall on the crash I had. I don't know if they would have done as well on the sides of the cowl as they are now mounted.

hehehe,, yup,,,
Just had my electrician bud pull apart a 5s3p lipo pack to reconfigure for a nice fit in the Chippy .
what he showed me was pretty darn scary ... 2 little flexible tabs VERY close together ,,,,if they touch , which I now see how easily they can ,,,, I shudder to think .. :eek:

take care ~

[thunder1]

I think the best packs come with a PC board to which the cells get soldered. A little more sturdy that way. But, I've had one case where the solder job done on the PC board was crappy and the solder tab on the cell unsoldered itself from the PC board! I was running that cell in a parallel configuration and the power dropped drastically. By the time I had landed the other pack had swelled up from being over discharged!

Have you seen this video from E-Flghtline of the 63" Super Chipmunk? It's good inspiration.
http://www.e-flightline.com/movies/Chipmunk%203.wmv

[thunder1]

I set the CG on the Sukhoi to 95mm and it flew great. A totally different plane. Rolls are very axial and it glided perfectly. I could give it full elevator deflection (+10mm) without it snapping and so I didn't have to worry about landing it.

The main change of Cg was accomplished by using the Cyclon 60 motor which is 2 ounces heavier than the AXI. I mounted it in reverse on the same mount as the AXI. The Cyclon 60 has a lower KV than the AXI but much more torque. I flew it on the same 5s2p pack but used a 13x8 prop. It gave me plenty of speed but not unlimited vertical. The motor was pretty hot after 10 minutes but the batteries were only warm so I could probably get more power out of it. I'm probably only putting 500 watts to the prop with the 13x8. I'm going to try a 14x7 to see if I can get better vertical. I also have a 3 bladed 12x6 prop and I'll try that one as well.

It's amazing how much stability can be affected by the CG being just a few mm off.

[the Swamp Fox]

Sweet :D

Glad to hear you've got her dialed in.

here's to many great flights .

~

[thunder1]

It's really a blast to fly. It's durable too. I had a hard landing yesterday when a gust of wind slammed it to the ground on landing. No damage except the gear was slightly bent. But I've got to get better vertical. I ordered a Phx HV-45 last night after I read the Phx 45 I have doesn't work reliably at more than 20 volts. I'm going to try a 6s2p setup for 800 watts!

[CUBANO8]

I ordered a Phx HV-45 last night


Thunder1,

Make sure you test out that HV-45, I bought 2 of them and the 1st one only lasted for 10 flights. I didn't find anything burned in it. I'm using a test plane for this purpose, the WM supersport 40. I've got 2 flights on the 2nd one, and so far so good. I've also tested a GP 45 brushless ESC, that is rated at 500watts, and that is exactly what my WOT gives, using my super whattmeter. 5 min in the flight the ESC started to fail, the motor stopped, and we had to throttle down for 3 seconds, then throttle back up for it to start up again.
I sent the HV-45 in for repair, and I also started a thread on the CC forum, but up to now they haven't replied to it directly, to answer my questions.

So if you have a plane to test it with, try going that route 1st.

Good Luck,
Sam :)

[the Swamp Fox]

I'm going to try a 6s2p setup for 800 watts!

that should do it :D

I was going to ask for a report on the new CC HV series as they're a little cheaper... and along comes Sam ! I'm using a test plane for this purpose, the WM supersport 40.

must be nice :)

Thanks for the info .. I'm sure they'll sort any issues out ,,,but for now I'll trust my models with Jeti and Hacker ESC ,,,but I'm sure people have had problems with those ;)

take care all ~

[thunder1]

Sam, Ack! Your ESC failed on the ground, right? You've got my knees knocking already! I crashed my 57" Super Chipmunk to a faulty ESC/Rx combo. Not sure which was the actual culprit. But both were damaged in the ensuing crash. I don't want to crash any more models to faulty equipment.

[CUBANO8]

Sam, Ack! Your ESC failed on the ground, right? You've got my knees knocking already! I crashed my 57" Super Chipmunk to a faulty ESC/Rx combo. Not sure which was the actual culprit. But both were damaged in the ensuing crash. I don't want to crash any more models to faulty equipment.

Yes, it failed on the ground, and not in the air, but I'm using a seperate rx pack, so at least I would have some control, in an event it does fail in the air.
That WM plane is a floater, so I shouldn't have problems, getting it back down.
Get yourself a test plane something cheap and use it there.

I eventually will use my HV-45 on a twin, so in an event of a failure, it will sure be fatal for that plane. Thats why i'm going to test it alot.

[CUBANO8]

Thanks for the info .. I'm sure they'll sort any issues out ,,,but for now I'll trust my models with Jeti and Hacker ESC

Yea, I'm sure they'll get it sorted out eventually.

I'm also going to be testing these:
http://www.balsapr.com/catalog/speedc/speedControllersBrushlessView.asp?ProductId=V47015 6

My friend Herm has ordered one, should be here next week.

[thunder1]

Good price on that BP ESC. It only goes up to 5s so it's basically in the same class as the Phx-45.

About the HV-45 dieing, I remember gettting a Phx 10 which died when I plugged it in. There was some bug in the firmware chip that if you got a bad contact plugging it in to the battery and the chip was powered on for less than a second or so the firmware would be erased. Sounds like a similar "feature"

[GregG]

Here's my Sukhoi Su-31 I converted to electric. It is from Black Horse Models but I believe it's the same as the Pheonix Models Su-31. The model is extremely sturdy. Originally designed for a .46 glow motor I decided to try out the AXI 2826/10 motor I already had with 4s2p 4000 mAH lipos. It turned out to be about 6 lbs so the power is pretty marginal with the mid size AXI. I'm pushing 500 watts through it but that's still not enough for a Sukhoi. .....

Which prop were you using with the 2826/10?

The reason I ask is that I just started using the same motor running on a 14-3700Nimh pack. The plane is a 91 oz ARF and has plenty of power. It'll go vertical just about anytime during a flight. Perhpas you just didn't have it prop matched?

[thunder1]

GregG,

I am using either an 11x7 APC E 12x6 APC E prop on my 2826/10 with 4s2p 4000mAH lipos. Static draw is around 40 amps for both. You must be pulling major amps running 14 cells. What prop are you using? Model Motors lists the 2826/10 as drawing 47 amps with 14 cells and an 11x8 prop.

I get plenty of vertical using the 2826/10 in my 57" Super Chipmunk. But not prop-hanging ability which is what I was after in the Sukhoi. I've since sold the model to a guy who put a .46 glow motor in it. He doesn't have enough power to prop hang either. The model really needs something like a .60 glow motor to prop hang. But again, it has such a high wing loading powered that way it doesn't make a good 3D model, which is why I sold it.